TimezoneArray.php

<?php

if (!function_exists('timezoneArray')) {

  /**
   * description
   *
   * @param
   * @return
   */
  function timezoneArray($regions = ["africa", "america", "antarctica", "asia", "atlantic", "australia", "europe", "indian", "pacific"], $detailed = true)
  {
    static $zones = [];
    foreach ($regions as $region) {
      if (strtoupper($region) == "AFRICA") {
        array_push($zones, DateTimeZone::AFRICA);
      } else if (strtoupper($region) == "AMERICA") {
        array_push($zones, DateTimeZone::AMERICA);
      } else if (strtoupper($region) == "ANTARCTICA") {
        array_push($zones, DateTimeZone::ANTARCTICA);
      } else if (strtoupper($region) == "ASIA") {
        array_push($zones, DateTimeZone::ASIA);
      } else if (strtoupper($region) == "ATLANTIC") {
        array_push($zones, DateTimeZone::ATLANTIC);
      } else if (strtoupper($region) == "AUSTRALIA") {
        array_push($zones, DateTimeZone::AUSTRALIA);
      } else if (strtoupper($region) == "EUROPE") {
        array_push($zones, DateTimeZone::EUROPE);
      } else if (strtoupper($region) == "INDIAN") {
        array_push($zones, DateTimeZone::INDIAN);
      } else if (strtoupper($region) == "PACIFIC") {
        array_push($zones, DateTimeZone::PACIFIC);
      }

      $timezones = array();
      foreach( $zones as $zone )
      {
        $timezones = array_merge( $timezones, DateTimeZone::listIdentifiers( $zone ) );
      }

      $timezone_offsets = array();
      foreach( $timezones as $timezone )
      {
        $tz = new DateTimeZone($timezone);
        $timezone_offsets[$timezone] = $tz->getOffset(new DateTime);
      }

      // sort timezone by offset
      asort($timezone_offsets);

      $timezone_list = array();
      foreach( $timezone_offsets as $timezone => $offset )
      {
          $offset_prefix = $offset < 0 ? '-' : '+';
          $offset_formatted = gmdate( 'H:i', abs($offset) );

          $pretty_offset = "UTC${offset_prefix}${offset_formatted}";

          if ($detailed) {
            $timezoneFormatted = $timezone;
          } else {
            $tzFormat = explode('/', $timezone, 2);
            $timezoneFormatted = $tzFormat[1];
          }
          $timezone_list[$timezone] = "(${pretty_offset}) $timezoneFormatted";

      }
    }
    return $timezone_list;
  }
}

This generates an array like:

array(
  "America/Denver" => "(UTC - 6:00) America/Denver"
  "America/Phoenix" => "(UTC - 6:00) America/Phoenix"
  ...
);

or if you pass false in the second parameter then you get:

array(
  "America/Denver" => "(UTC - 6:00) Denver"
  "America/Phoenix" => "(UTC - 6:00) Phoenix"
  ...
);